Turkey must uphold its side of a deal made with the European Union over stemming the flow of migrants, a top EU official said Thursday, warning "threats" against the bloc will not work.

Turkey must uphold its side of a deal made with the European Union over stemming the flow of migrants, a top EU official said Thursday, warning "threats" against the bloc will not work.

European Commission President Jean-Claude Juncker said Ankara must ease strict anti-terror laws if it wants its citizens to enjoy visa-free travel on the continent.

Juncker was speaking after President Recep Tayyip Erdogan on Tuesday warned the European Union his parliament would block laws related to the landmark deal if it didn't get its way on visa liberalization.

"We do expect that Turkey will stick to its commitments -- and threats are not the best diplomatic instrument you can use," Juncker told reporters in Ise-Shima, where he is attending the G7 summit.

"So one should stop to use them, because they will produce no effect whatsoever."

Juncker's outburst came after Erdogan dug his heels in over growing indications that a deal to grant Turks the right to travel freely in Europe looked to be faltering.

Angela Merkel warned after talks with Erdogan on Monday that the target of an end-June implementation was unlikely to be met.

The agreement saw Turkey pledge to work to stop migrants crossing the Aegean to Europe and also readmit migrants who had crossed illegally.

EU officials hailed the success of the deal, but Ankara has grown increasingly uneasy about the bloc's wariness to grant it the visa-free travel to the passport free Schengen area it was offered in return.

"If that (the visa exemption) is not what will happen... no decision and no law in the framework of the readmission agreement will come out of the parliament of the Turkish Republic," Erdogan said at the close of the World Humanitarian Summit in Istanbul this week.

"Our foreign ministry, our EU affairs ministry will have discussions with the Europeans. If there is a result then great. If not, then I'm sorry."